Fix scrolling for large outputs

IPython/html/static/notebook/less/pager.less

@@ -8,6 +8,7 div#pager {
     bottom: 0px;
     width: 100%;
     border-top: 1px solid @navbar-default-border;
+    max-height: 50%;
 
     /* Display over codemirror */
     z-index: 100;

IPython/html/static/style/style.min.css

@@ -10289,6 +10289,7 div#pager {
   bottom: 0px;
   width: 100%;
   border-top: 1px solid #e7e7e7;
+  max-height: 50%;
   /* Display over codemirror */
   z-index: 100;
   /* Hack which prevents jquery ui resizable from changing top. */